<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html lang="en">
<head>
<title>Source code</title>
<link rel="stylesheet" type="text/css" href="../../../../../stylesheet.css" title="Style">
</head>
<body>
<div class="sourceContainer">
<pre><span class="sourceLineNo">001</span>/*<a name="line.1"></a>
<span class="sourceLineNo">002</span> * Copyright (C) 2007 The Guava Authors<a name="line.2"></a>
<span class="sourceLineNo">003</span> *<a name="line.3"></a>
<span class="sourceLineNo">004</span> * Licensed under the Apache License, Version 2.0 (the "License");<a name="line.4"></a>
<span class="sourceLineNo">005</span> * you may not use this file except in compliance with the License.<a name="line.5"></a>
<span class="sourceLineNo">006</span> * You may obtain a copy of the License at<a name="line.6"></a>
<span class="sourceLineNo">007</span> *<a name="line.7"></a>
<span class="sourceLineNo">008</span> * http://www.apache.org/licenses/LICENSE-2.0<a name="line.8"></a>
<span class="sourceLineNo">009</span> *<a name="line.9"></a>
<span class="sourceLineNo">010</span> * Unless required by applicable law or agreed to in writing, software<a name="line.10"></a>
<span class="sourceLineNo">011</span> * distributed under the License is distributed on an "AS IS" BASIS,<a name="line.11"></a>
<span class="sourceLineNo">012</span> * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.<a name="line.12"></a>
<span class="sourceLineNo">013</span> * See the License for the specific language governing permissions and<a name="line.13"></a>
<span class="sourceLineNo">014</span> * limitations under the License.<a name="line.14"></a>
<span class="sourceLineNo">015</span> */<a name="line.15"></a>
<span class="sourceLineNo">016</span><a name="line.16"></a>
<span class="sourceLineNo">017</span>package com.google.common.base;<a name="line.17"></a>
<span class="sourceLineNo">018</span><a name="line.18"></a>
<span class="sourceLineNo">019</span>import com.google.common.annotations.Beta;<a name="line.19"></a>
<span class="sourceLineNo">020</span>import com.google.common.annotations.GwtCompatible;<a name="line.20"></a>
<span class="sourceLineNo">021</span>import com.google.common.annotations.VisibleForTesting;<a name="line.21"></a>
<span class="sourceLineNo">022</span><a name="line.22"></a>
<span class="sourceLineNo">023</span>import java.io.Serializable;<a name="line.23"></a>
<span class="sourceLineNo">024</span>import java.util.concurrent.TimeUnit;<a name="line.24"></a>
<span class="sourceLineNo">025</span><a name="line.25"></a>
<span class="sourceLineNo">026</span>import javax.annotation.Nullable;<a name="line.26"></a>
<span class="sourceLineNo">027</span><a name="line.27"></a>
<span class="sourceLineNo">028</span>/**<a name="line.28"></a>
<span class="sourceLineNo">029</span> * Useful suppliers.<a name="line.29"></a>
<span class="sourceLineNo">030</span> *<a name="line.30"></a>
<span class="sourceLineNo">031</span> * &lt;p&gt;All methods return serializable suppliers as long as they're given<a name="line.31"></a>
<span class="sourceLineNo">032</span> * serializable parameters.<a name="line.32"></a>
<span class="sourceLineNo">033</span> *<a name="line.33"></a>
<span class="sourceLineNo">034</span> * @author Laurence Gonsalves<a name="line.34"></a>
<span class="sourceLineNo">035</span> * @author Harry Heymann<a name="line.35"></a>
<span class="sourceLineNo">036</span> * @since 2.0 (imported from Google Collections Library)<a name="line.36"></a>
<span class="sourceLineNo">037</span> */<a name="line.37"></a>
<span class="sourceLineNo">038</span>@GwtCompatible<a name="line.38"></a>
<span class="sourceLineNo">039</span>public final class Suppliers {<a name="line.39"></a>
<span class="sourceLineNo">040</span>  private Suppliers() {}<a name="line.40"></a>
<span class="sourceLineNo">041</span><a name="line.41"></a>
<span class="sourceLineNo">042</span>  /**<a name="line.42"></a>
<span class="sourceLineNo">043</span>   * Returns a new supplier which is the composition of the provided function<a name="line.43"></a>
<span class="sourceLineNo">044</span>   * and supplier. In other words, the new supplier's value will be computed by<a name="line.44"></a>
<span class="sourceLineNo">045</span>   * retrieving the value from {@code supplier}, and then applying<a name="line.45"></a>
<span class="sourceLineNo">046</span>   * {@code function} to that value. Note that the resulting supplier will not<a name="line.46"></a>
<span class="sourceLineNo">047</span>   * call {@code supplier} or invoke {@code function} until it is called.<a name="line.47"></a>
<span class="sourceLineNo">048</span>   */<a name="line.48"></a>
<span class="sourceLineNo">049</span>  public static &lt;F, T&gt; Supplier&lt;T&gt; compose(<a name="line.49"></a>
<span class="sourceLineNo">050</span>      Function&lt;? super F, T&gt; function, Supplier&lt;F&gt; supplier) {<a name="line.50"></a>
<span class="sourceLineNo">051</span>    Preconditions.checkNotNull(function);<a name="line.51"></a>
<span class="sourceLineNo">052</span>    Preconditions.checkNotNull(supplier);<a name="line.52"></a>
<span class="sourceLineNo">053</span>    return new SupplierComposition&lt;F, T&gt;(function, supplier);<a name="line.53"></a>
<span class="sourceLineNo">054</span>  }<a name="line.54"></a>
<span class="sourceLineNo">055</span><a name="line.55"></a>
<span class="sourceLineNo">056</span>  private static class SupplierComposition&lt;F, T&gt;<a name="line.56"></a>
<span class="sourceLineNo">057</span>      implements Supplier&lt;T&gt;, Serializable {<a name="line.57"></a>
<span class="sourceLineNo">058</span>    final Function&lt;? super F, T&gt; function;<a name="line.58"></a>
<span class="sourceLineNo">059</span>    final Supplier&lt;F&gt; supplier;<a name="line.59"></a>
<span class="sourceLineNo">060</span><a name="line.60"></a>
<span class="sourceLineNo">061</span>    SupplierComposition(Function&lt;? super F, T&gt; function, Supplier&lt;F&gt; supplier) {<a name="line.61"></a>
<span class="sourceLineNo">062</span>      this.function = function;<a name="line.62"></a>
<span class="sourceLineNo">063</span>      this.supplier = supplier;<a name="line.63"></a>
<span class="sourceLineNo">064</span>    }<a name="line.64"></a>
<span class="sourceLineNo">065</span><a name="line.65"></a>
<span class="sourceLineNo">066</span>    @Override public T get() {<a name="line.66"></a>
<span class="sourceLineNo">067</span>      return function.apply(supplier.get());<a name="line.67"></a>
<span class="sourceLineNo">068</span>    }<a name="line.68"></a>
<span class="sourceLineNo">069</span><a name="line.69"></a>
<span class="sourceLineNo">070</span>    @Override public boolean equals(@Nullable Object obj) {<a name="line.70"></a>
<span class="sourceLineNo">071</span>      if (obj instanceof SupplierComposition) {<a name="line.71"></a>
<span class="sourceLineNo">072</span>        SupplierComposition&lt;?, ?&gt; that = (SupplierComposition&lt;?, ?&gt;) obj;<a name="line.72"></a>
<span class="sourceLineNo">073</span>        return function.equals(that.function) &amp;&amp; supplier.equals(that.supplier);<a name="line.73"></a>
<span class="sourceLineNo">074</span>      }<a name="line.74"></a>
<span class="sourceLineNo">075</span>      return false;<a name="line.75"></a>
<span class="sourceLineNo">076</span>    }<a name="line.76"></a>
<span class="sourceLineNo">077</span><a name="line.77"></a>
<span class="sourceLineNo">078</span>    @Override public int hashCode() {<a name="line.78"></a>
<span class="sourceLineNo">079</span>      return Objects.hashCode(function, supplier);<a name="line.79"></a>
<span class="sourceLineNo">080</span>    }<a name="line.80"></a>
<span class="sourceLineNo">081</span><a name="line.81"></a>
<span class="sourceLineNo">082</span>    @Override public String toString() {<a name="line.82"></a>
<span class="sourceLineNo">083</span>      return "Suppliers.compose(" + function + ", " + supplier + ")";<a name="line.83"></a>
<span class="sourceLineNo">084</span>    }<a name="line.84"></a>
<span class="sourceLineNo">085</span><a name="line.85"></a>
<span class="sourceLineNo">086</span>    private static final long serialVersionUID = 0;<a name="line.86"></a>
<span class="sourceLineNo">087</span>  }<a name="line.87"></a>
<span class="sourceLineNo">088</span><a name="line.88"></a>
<span class="sourceLineNo">089</span>  /**<a name="line.89"></a>
<span class="sourceLineNo">090</span>   * Returns a supplier which caches the instance retrieved during the first<a name="line.90"></a>
<span class="sourceLineNo">091</span>   * call to {@code get()} and returns that value on subsequent calls to<a name="line.91"></a>
<span class="sourceLineNo">092</span>   * {@code get()}. See:<a name="line.92"></a>
<span class="sourceLineNo">093</span>   * &lt;a href="http://en.wikipedia.org/wiki/Memoization"&gt;memoization&lt;/a&gt;<a name="line.93"></a>
<span class="sourceLineNo">094</span>   *<a name="line.94"></a>
<span class="sourceLineNo">095</span>   * &lt;p&gt;The returned supplier is thread-safe. The supplier's serialized form<a name="line.95"></a>
<span class="sourceLineNo">096</span>   * does not contain the cached value, which will be recalculated when {@code<a name="line.96"></a>
<span class="sourceLineNo">097</span>   * get()} is called on the reserialized instance.<a name="line.97"></a>
<span class="sourceLineNo">098</span>   *<a name="line.98"></a>
<span class="sourceLineNo">099</span>   * &lt;p&gt;If {@code delegate} is an instance created by an earlier call to {@code<a name="line.99"></a>
<span class="sourceLineNo">100</span>   * memoize}, it is returned directly.<a name="line.100"></a>
<span class="sourceLineNo">101</span>   */<a name="line.101"></a>
<span class="sourceLineNo">102</span>  public static &lt;T&gt; Supplier&lt;T&gt; memoize(Supplier&lt;T&gt; delegate) {<a name="line.102"></a>
<span class="sourceLineNo">103</span>    return (delegate instanceof MemoizingSupplier)<a name="line.103"></a>
<span class="sourceLineNo">104</span>        ? delegate<a name="line.104"></a>
<span class="sourceLineNo">105</span>        : new MemoizingSupplier&lt;T&gt;(Preconditions.checkNotNull(delegate));<a name="line.105"></a>
<span class="sourceLineNo">106</span>  }<a name="line.106"></a>
<span class="sourceLineNo">107</span><a name="line.107"></a>
<span class="sourceLineNo">108</span>  @VisibleForTesting<a name="line.108"></a>
<span class="sourceLineNo">109</span>  static class MemoizingSupplier&lt;T&gt; implements Supplier&lt;T&gt;, Serializable {<a name="line.109"></a>
<span class="sourceLineNo">110</span>    final Supplier&lt;T&gt; delegate;<a name="line.110"></a>
<span class="sourceLineNo">111</span>    transient volatile boolean initialized;<a name="line.111"></a>
<span class="sourceLineNo">112</span>    // "value" does not need to be volatile; visibility piggy-backs<a name="line.112"></a>
<span class="sourceLineNo">113</span>    // on volatile read of "initialized".<a name="line.113"></a>
<span class="sourceLineNo">114</span>    transient T value;<a name="line.114"></a>
<span class="sourceLineNo">115</span><a name="line.115"></a>
<span class="sourceLineNo">116</span>    MemoizingSupplier(Supplier&lt;T&gt; delegate) {<a name="line.116"></a>
<span class="sourceLineNo">117</span>      this.delegate = delegate;<a name="line.117"></a>
<span class="sourceLineNo">118</span>    }<a name="line.118"></a>
<span class="sourceLineNo">119</span><a name="line.119"></a>
<span class="sourceLineNo">120</span>    @Override public T get() {<a name="line.120"></a>
<span class="sourceLineNo">121</span>      // A 2-field variant of Double Checked Locking.<a name="line.121"></a>
<span class="sourceLineNo">122</span>      if (!initialized) {<a name="line.122"></a>
<span class="sourceLineNo">123</span>        synchronized (this) {<a name="line.123"></a>
<span class="sourceLineNo">124</span>          if (!initialized) {<a name="line.124"></a>
<span class="sourceLineNo">125</span>            T t = delegate.get();<a name="line.125"></a>
<span class="sourceLineNo">126</span>            value = t;<a name="line.126"></a>
<span class="sourceLineNo">127</span>            initialized = true;<a name="line.127"></a>
<span class="sourceLineNo">128</span>            return t;<a name="line.128"></a>
<span class="sourceLineNo">129</span>          }<a name="line.129"></a>
<span class="sourceLineNo">130</span>        }<a name="line.130"></a>
<span class="sourceLineNo">131</span>      }<a name="line.131"></a>
<span class="sourceLineNo">132</span>      return value;<a name="line.132"></a>
<span class="sourceLineNo">133</span>    }<a name="line.133"></a>
<span class="sourceLineNo">134</span><a name="line.134"></a>
<span class="sourceLineNo">135</span>    @Override public String toString() {<a name="line.135"></a>
<span class="sourceLineNo">136</span>      return "Suppliers.memoize(" + delegate + ")";<a name="line.136"></a>
<span class="sourceLineNo">137</span>    }<a name="line.137"></a>
<span class="sourceLineNo">138</span><a name="line.138"></a>
<span class="sourceLineNo">139</span>    private static final long serialVersionUID = 0;<a name="line.139"></a>
<span class="sourceLineNo">140</span>  }<a name="line.140"></a>
<span class="sourceLineNo">141</span><a name="line.141"></a>
<span class="sourceLineNo">142</span>  /**<a name="line.142"></a>
<span class="sourceLineNo">143</span>   * Returns a supplier that caches the instance supplied by the delegate and<a name="line.143"></a>
<span class="sourceLineNo">144</span>   * removes the cached value after the specified time has passed. Subsequent<a name="line.144"></a>
<span class="sourceLineNo">145</span>   * calls to {@code get()} return the cached value if the expiration time has<a name="line.145"></a>
<span class="sourceLineNo">146</span>   * not passed. After the expiration time, a new value is retrieved, cached,<a name="line.146"></a>
<span class="sourceLineNo">147</span>   * and returned. See:<a name="line.147"></a>
<span class="sourceLineNo">148</span>   * &lt;a href="http://en.wikipedia.org/wiki/Memoization"&gt;memoization&lt;/a&gt;<a name="line.148"></a>
<span class="sourceLineNo">149</span>   *<a name="line.149"></a>
<span class="sourceLineNo">150</span>   * &lt;p&gt;The returned supplier is thread-safe. The supplier's serialized form<a name="line.150"></a>
<span class="sourceLineNo">151</span>   * does not contain the cached value, which will be recalculated when {@code<a name="line.151"></a>
<span class="sourceLineNo">152</span>   * get()} is called on the reserialized instance.<a name="line.152"></a>
<span class="sourceLineNo">153</span>   *<a name="line.153"></a>
<span class="sourceLineNo">154</span>   * @param duration the length of time after a value is created that it<a name="line.154"></a>
<span class="sourceLineNo">155</span>   *     should stop being returned by subsequent {@code get()} calls<a name="line.155"></a>
<span class="sourceLineNo">156</span>   * @param unit the unit that {@code duration} is expressed in<a name="line.156"></a>
<span class="sourceLineNo">157</span>   * @throws IllegalArgumentException if {@code duration} is not positive<a name="line.157"></a>
<span class="sourceLineNo">158</span>   * @since 2.0<a name="line.158"></a>
<span class="sourceLineNo">159</span>   */<a name="line.159"></a>
<span class="sourceLineNo">160</span>  public static &lt;T&gt; Supplier&lt;T&gt; memoizeWithExpiration(<a name="line.160"></a>
<span class="sourceLineNo">161</span>      Supplier&lt;T&gt; delegate, long duration, TimeUnit unit) {<a name="line.161"></a>
<span class="sourceLineNo">162</span>    return new ExpiringMemoizingSupplier&lt;T&gt;(delegate, duration, unit);<a name="line.162"></a>
<span class="sourceLineNo">163</span>  }<a name="line.163"></a>
<span class="sourceLineNo">164</span><a name="line.164"></a>
<span class="sourceLineNo">165</span>  @VisibleForTesting static class ExpiringMemoizingSupplier&lt;T&gt;<a name="line.165"></a>
<span class="sourceLineNo">166</span>      implements Supplier&lt;T&gt;, Serializable {<a name="line.166"></a>
<span class="sourceLineNo">167</span>    final Supplier&lt;T&gt; delegate;<a name="line.167"></a>
<span class="sourceLineNo">168</span>    final long durationNanos;<a name="line.168"></a>
<span class="sourceLineNo">169</span>    transient volatile T value;<a name="line.169"></a>
<span class="sourceLineNo">170</span>    // The special value 0 means "not yet initialized".<a name="line.170"></a>
<span class="sourceLineNo">171</span>    transient volatile long expirationNanos;<a name="line.171"></a>
<span class="sourceLineNo">172</span><a name="line.172"></a>
<span class="sourceLineNo">173</span>    ExpiringMemoizingSupplier(<a name="line.173"></a>
<span class="sourceLineNo">174</span>        Supplier&lt;T&gt; delegate, long duration, TimeUnit unit) {<a name="line.174"></a>
<span class="sourceLineNo">175</span>      this.delegate = Preconditions.checkNotNull(delegate);<a name="line.175"></a>
<span class="sourceLineNo">176</span>      this.durationNanos = unit.toNanos(duration);<a name="line.176"></a>
<span class="sourceLineNo">177</span>      Preconditions.checkArgument(duration &gt; 0);<a name="line.177"></a>
<span class="sourceLineNo">178</span>    }<a name="line.178"></a>
<span class="sourceLineNo">179</span><a name="line.179"></a>
<span class="sourceLineNo">180</span>    @Override public T get() {<a name="line.180"></a>
<span class="sourceLineNo">181</span>      // Another variant of Double Checked Locking.<a name="line.181"></a>
<span class="sourceLineNo">182</span>      //<a name="line.182"></a>
<span class="sourceLineNo">183</span>      // We use two volatile reads.  We could reduce this to one by<a name="line.183"></a>
<span class="sourceLineNo">184</span>      // putting our fields into a holder class, but (at least on x86)<a name="line.184"></a>
<span class="sourceLineNo">185</span>      // the extra memory consumption and indirection are more<a name="line.185"></a>
<span class="sourceLineNo">186</span>      // expensive than the extra volatile reads.<a name="line.186"></a>
<span class="sourceLineNo">187</span>      long nanos = expirationNanos;<a name="line.187"></a>
<span class="sourceLineNo">188</span>      long now = Platform.systemNanoTime();<a name="line.188"></a>
<span class="sourceLineNo">189</span>      if (nanos == 0 || now - nanos &gt;= 0) {<a name="line.189"></a>
<span class="sourceLineNo">190</span>        synchronized (this) {<a name="line.190"></a>
<span class="sourceLineNo">191</span>          if (nanos == expirationNanos) {  // recheck for lost race<a name="line.191"></a>
<span class="sourceLineNo">192</span>            T t = delegate.get();<a name="line.192"></a>
<span class="sourceLineNo">193</span>            value = t;<a name="line.193"></a>
<span class="sourceLineNo">194</span>            nanos = now + durationNanos;<a name="line.194"></a>
<span class="sourceLineNo">195</span>            // In the very unlikely event that nanos is 0, set it to 1;<a name="line.195"></a>
<span class="sourceLineNo">196</span>            // no one will notice 1 ns of tardiness.<a name="line.196"></a>
<span class="sourceLineNo">197</span>            expirationNanos = (nanos == 0) ? 1 : nanos;<a name="line.197"></a>
<span class="sourceLineNo">198</span>            return t;<a name="line.198"></a>
<span class="sourceLineNo">199</span>          }<a name="line.199"></a>
<span class="sourceLineNo">200</span>        }<a name="line.200"></a>
<span class="sourceLineNo">201</span>      }<a name="line.201"></a>
<span class="sourceLineNo">202</span>      return value;<a name="line.202"></a>
<span class="sourceLineNo">203</span>    }<a name="line.203"></a>
<span class="sourceLineNo">204</span><a name="line.204"></a>
<span class="sourceLineNo">205</span>    @Override public String toString() {<a name="line.205"></a>
<span class="sourceLineNo">206</span>      // This is a little strange if the unit the user provided was not NANOS,<a name="line.206"></a>
<span class="sourceLineNo">207</span>      // but we don't want to store the unit just for toString<a name="line.207"></a>
<span class="sourceLineNo">208</span>      return "Suppliers.memoizeWithExpiration(" + delegate + ", " +<a name="line.208"></a>
<span class="sourceLineNo">209</span>          durationNanos + ", NANOS)";<a name="line.209"></a>
<span class="sourceLineNo">210</span>    }<a name="line.210"></a>
<span class="sourceLineNo">211</span><a name="line.211"></a>
<span class="sourceLineNo">212</span>    private static final long serialVersionUID = 0;<a name="line.212"></a>
<span class="sourceLineNo">213</span>  }<a name="line.213"></a>
<span class="sourceLineNo">214</span><a name="line.214"></a>
<span class="sourceLineNo">215</span>  /**<a name="line.215"></a>
<span class="sourceLineNo">216</span>   * Returns a supplier that always supplies {@code instance}.<a name="line.216"></a>
<span class="sourceLineNo">217</span>   */<a name="line.217"></a>
<span class="sourceLineNo">218</span>  public static &lt;T&gt; Supplier&lt;T&gt; ofInstance(@Nullable T instance) {<a name="line.218"></a>
<span class="sourceLineNo">219</span>    return new SupplierOfInstance&lt;T&gt;(instance);<a name="line.219"></a>
<span class="sourceLineNo">220</span>  }<a name="line.220"></a>
<span class="sourceLineNo">221</span><a name="line.221"></a>
<span class="sourceLineNo">222</span>  private static class SupplierOfInstance&lt;T&gt;<a name="line.222"></a>
<span class="sourceLineNo">223</span>      implements Supplier&lt;T&gt;, Serializable {<a name="line.223"></a>
<span class="sourceLineNo">224</span>    final T instance;<a name="line.224"></a>
<span class="sourceLineNo">225</span><a name="line.225"></a>
<span class="sourceLineNo">226</span>    SupplierOfInstance(@Nullable T instance) {<a name="line.226"></a>
<span class="sourceLineNo">227</span>      this.instance = instance;<a name="line.227"></a>
<span class="sourceLineNo">228</span>    }<a name="line.228"></a>
<span class="sourceLineNo">229</span><a name="line.229"></a>
<span class="sourceLineNo">230</span>    @Override public T get() {<a name="line.230"></a>
<span class="sourceLineNo">231</span>      return instance;<a name="line.231"></a>
<span class="sourceLineNo">232</span>    }<a name="line.232"></a>
<span class="sourceLineNo">233</span><a name="line.233"></a>
<span class="sourceLineNo">234</span>    @Override public boolean equals(@Nullable Object obj) {<a name="line.234"></a>
<span class="sourceLineNo">235</span>      if (obj instanceof SupplierOfInstance) {<a name="line.235"></a>
<span class="sourceLineNo">236</span>        SupplierOfInstance&lt;?&gt; that = (SupplierOfInstance&lt;?&gt;) obj;<a name="line.236"></a>
<span class="sourceLineNo">237</span>        return Objects.equal(instance, that.instance);<a name="line.237"></a>
<span class="sourceLineNo">238</span>      }<a name="line.238"></a>
<span class="sourceLineNo">239</span>      return false;<a name="line.239"></a>
<span class="sourceLineNo">240</span>    }<a name="line.240"></a>
<span class="sourceLineNo">241</span><a name="line.241"></a>
<span class="sourceLineNo">242</span>    @Override public int hashCode() {<a name="line.242"></a>
<span class="sourceLineNo">243</span>      return Objects.hashCode(instance);<a name="line.243"></a>
<span class="sourceLineNo">244</span>    }<a name="line.244"></a>
<span class="sourceLineNo">245</span><a name="line.245"></a>
<span class="sourceLineNo">246</span>    @Override public String toString() {<a name="line.246"></a>
<span class="sourceLineNo">247</span>      return "Suppliers.ofInstance(" + instance + ")";<a name="line.247"></a>
<span class="sourceLineNo">248</span>    }<a name="line.248"></a>
<span class="sourceLineNo">249</span><a name="line.249"></a>
<span class="sourceLineNo">250</span>    private static final long serialVersionUID = 0;<a name="line.250"></a>
<span class="sourceLineNo">251</span>  }<a name="line.251"></a>
<span class="sourceLineNo">252</span><a name="line.252"></a>
<span class="sourceLineNo">253</span>  /**<a name="line.253"></a>
<span class="sourceLineNo">254</span>   * Returns a supplier whose {@code get()} method synchronizes on<a name="line.254"></a>
<span class="sourceLineNo">255</span>   * {@code delegate} before calling it, making it thread-safe.<a name="line.255"></a>
<span class="sourceLineNo">256</span>   */<a name="line.256"></a>
<span class="sourceLineNo">257</span>  public static &lt;T&gt; Supplier&lt;T&gt; synchronizedSupplier(Supplier&lt;T&gt; delegate) {<a name="line.257"></a>
<span class="sourceLineNo">258</span>    return new ThreadSafeSupplier&lt;T&gt;(Preconditions.checkNotNull(delegate));<a name="line.258"></a>
<span class="sourceLineNo">259</span>  }<a name="line.259"></a>
<span class="sourceLineNo">260</span><a name="line.260"></a>
<span class="sourceLineNo">261</span>  private static class ThreadSafeSupplier&lt;T&gt;<a name="line.261"></a>
<span class="sourceLineNo">262</span>      implements Supplier&lt;T&gt;, Serializable {<a name="line.262"></a>
<span class="sourceLineNo">263</span>    final Supplier&lt;T&gt; delegate;<a name="line.263"></a>
<span class="sourceLineNo">264</span><a name="line.264"></a>
<span class="sourceLineNo">265</span>    ThreadSafeSupplier(Supplier&lt;T&gt; delegate) {<a name="line.265"></a>
<span class="sourceLineNo">266</span>      this.delegate = delegate;<a name="line.266"></a>
<span class="sourceLineNo">267</span>    }<a name="line.267"></a>
<span class="sourceLineNo">268</span><a name="line.268"></a>
<span class="sourceLineNo">269</span>    @Override public T get() {<a name="line.269"></a>
<span class="sourceLineNo">270</span>      synchronized (delegate) {<a name="line.270"></a>
<span class="sourceLineNo">271</span>        return delegate.get();<a name="line.271"></a>
<span class="sourceLineNo">272</span>      }<a name="line.272"></a>
<span class="sourceLineNo">273</span>    }<a name="line.273"></a>
<span class="sourceLineNo">274</span><a name="line.274"></a>
<span class="sourceLineNo">275</span>    @Override public String toString() {<a name="line.275"></a>
<span class="sourceLineNo">276</span>      return "Suppliers.synchronizedSupplier(" + delegate + ")";<a name="line.276"></a>
<span class="sourceLineNo">277</span>    }<a name="line.277"></a>
<span class="sourceLineNo">278</span><a name="line.278"></a>
<span class="sourceLineNo">279</span>    private static final long serialVersionUID = 0;<a name="line.279"></a>
<span class="sourceLineNo">280</span>  }<a name="line.280"></a>
<span class="sourceLineNo">281</span><a name="line.281"></a>
<span class="sourceLineNo">282</span>  /**<a name="line.282"></a>
<span class="sourceLineNo">283</span>   * Returns a function that accepts a supplier and returns the result of<a name="line.283"></a>
<span class="sourceLineNo">284</span>   * invoking {@link Supplier#get} on that supplier.<a name="line.284"></a>
<span class="sourceLineNo">285</span>   *<a name="line.285"></a>
<span class="sourceLineNo">286</span>   * @since 8.0<a name="line.286"></a>
<span class="sourceLineNo">287</span>   */<a name="line.287"></a>
<span class="sourceLineNo">288</span>  @Beta<a name="line.288"></a>
<span class="sourceLineNo">289</span>  //SupplierFunction works for any T.<a name="line.289"></a>
<span class="sourceLineNo">290</span>  @SuppressWarnings({"unchecked", "rawtypes"})<a name="line.290"></a>
<span class="sourceLineNo">291</span>  public static &lt;T&gt; Function&lt;Supplier&lt;T&gt;, T&gt; supplierFunction() {<a name="line.291"></a>
<span class="sourceLineNo">292</span>    return (Function) SupplierFunction.INSTANCE;<a name="line.292"></a>
<span class="sourceLineNo">293</span>  }<a name="line.293"></a>
<span class="sourceLineNo">294</span><a name="line.294"></a>
<span class="sourceLineNo">295</span>  private enum SupplierFunction implements Function&lt;Supplier&lt;?&gt;, Object&gt; {<a name="line.295"></a>
<span class="sourceLineNo">296</span>    INSTANCE;<a name="line.296"></a>
<span class="sourceLineNo">297</span><a name="line.297"></a>
<span class="sourceLineNo">298</span>    @Override public Object apply(Supplier&lt;?&gt; input) {<a name="line.298"></a>
<span class="sourceLineNo">299</span>      return input.get();<a name="line.299"></a>
<span class="sourceLineNo">300</span>    }<a name="line.300"></a>
<span class="sourceLineNo">301</span><a name="line.301"></a>
<span class="sourceLineNo">302</span>    @Override public String toString() {<a name="line.302"></a>
<span class="sourceLineNo">303</span>      return "Suppliers.supplierFunction()";<a name="line.303"></a>
<span class="sourceLineNo">304</span>    }<a name="line.304"></a>
<span class="sourceLineNo">305</span>  }<a name="line.305"></a>
<span class="sourceLineNo">306</span>}<a name="line.306"></a>




























































</pre>
</div>
</body>
</html>
